Le 03/08/2023 à 10:46, Guillaume Nault a écrit :
> On Wed, Aug 02, 2023 at 02:21:06PM +0200, Nicolas Dichtel wrote:
>> This kind of interface doesn't have a mac header.
>
> Well, PPP does have a link layer header.
It has a link layer, but not an ethernet header.
> Do you instead mean that PPP automatically adds it?
>
>> This patch fixes bpf_redirect() to a ppp interface.
>
> Can you give more details? Which kind of packets are you trying to
> redirect to PPP interfaces?
My ebpf program redirect an IP packet (eth / ip) from a physical ethernet device
at ingress to a ppp device at egress. In this case, the bpf_redirect() function
should remove the ethernet header from the packet before calling the xmit ppp
function. Before my patch, the ppp xmit function adds a ppp header (protocol IP
/ 0x0021) before the ethernet header. It results to a corrupted packet. After
the patch, the ppp xmit function encapsulates the IP packet, as expected.
>
> To me this looks like a hack to work around the fact that
> ppp_start_xmit() automatically adds a PPP header. Maybe that's the
It's not an hack, it works like for other kind of devices managed by the
function bpf_redirect() / dev_is_mac_header_xmit().
Hope it's more clear.
Regards,
Nicolas
> best we can do given the current state of ppp_generic.c, but the
> commit message should be clear about what the real problem is and
> why the patch takes this approach to fix or work around it.
>
>> CC: stable@xxxxxxxxxxxxxxx
>> Fixes: 27b29f63058d ("bpf: add bpf_redirect() helper")
>> Signed-off-by: Nicolas Dichtel <nicolas.dichtel@xxxxxxxxx>
>> Tested-by: Siwar Zitouni <siwar.zitouni@xxxxxxxxx>
>> ---
>>
>> v1 -> v2:
>> - I forgot the 'Tested-by' tag in the v1 :/
>>
>> include/linux/if_arp.h | 1 +
>> 1 file changed, 1 insertion(+)
>>
>> diff --git a/include/linux/if_arp.h b/include/linux/if_arp.h
>> index 1ed52441972f..8efbe29a6f0c 100644
>> --- a/include/linux/if_arp.h
>> +++ b/include/linux/if_arp.h
>> @@ -53,6 +53,7 @@ static inline bool dev_is_mac_header_xmit(const struct net_device *dev)
>> case ARPHRD_NONE:
>> case ARPHRD_RAWIP:
>> case ARPHRD_PIMREG:
>> + case ARPHRD_PPP:
>> return false;
>> default:
>> return true;
>> --
>> 2.39.2
>>
>>
>
